Solid bipropellant

ABSTRACT

A solid bipropellant grain having a specific impulse of over 275 seconds comprising a slotted, single perforate, internal burning oxidizer grain and adjacent pressed lithium aluminum hydride plates in which the greatest surface is exposed to the flow of the combustion products of the oxidant.

United States Patent v 1 Thrailkill et al. [451 Mar. 27, 1973 [54] SOLIDBIPROPELLANT 2,759,418 8/1956 Ross et al. ..149/74 X 9 5 751 Inventors:Arthur E. Thrailkill, Bel Air; Robert w Geene Aberdeen bothofMd ox2,977,885 4/1961 Perry et a1. ..149/15 [73] Assignee: The United Statesof America as represented by the Secretary of t PrimaryExaminer-Benjamin R. Padgett y Attorney-S. J. Rotondi and A. T. Dupont[22] Filed: Apr. 4, 1962 CT 57 ABSTRA [21] Appl. No.: 185,185

A solid bipropellant grain having a specific impulse of U S Cl 102/101149/2 149/15 over 275 seconds comprising a slotted, single per- 511 Int. C1 I C06d 5706 F4 2b 1/00 Mate internal burning Miler grain andmil-em [58] Field of se;; ii 149/15 14 2- 60/354 Pressed lithiumaluminum hydride Plates in which 1 2 greatest surface is exposed to theflow of the combustion products of the oxidant.

[5 6] References Cited UNITED STATES PATENTS 2 Claims, 3 Drawing Figures2,408,252 9/1946 DeGanahl ..102 9s h o /der SOLID BIPROPELLANT Theinvention described herein may be manufactured and used by or for theGovernment for govemmental purposes without the payment to us of anyroyalty thereon.

The present invention relates to solid propellants for rockets andmissiles which are composed of two essentially incompatible materialswhich will not react until a designated time.

The primary object of this invention is to combine highly reactivecomponents into a high energy solid propellant grain.

Another object of this invention is to combine a powerful reducing agentwith a powerful oxidizing agent and produce a propellant grain which issafe from failure. I I

A further object of this invention is to combine the highly reactivefuel and oxidizer components of a propellant grain in such a manner thatthe components will react in an efficient manner.

Other and further objects and advantages of this invention will becomeapparent to those skilled in the art from the following specificationand claims taken in connection with the accompanying drawing.

Practical embodiments of the present invention may be furtherillustrated by the accompanying drawing, wherein:

FIG. 1 illustrates one embodiment whereby the twelve spoke wheel fuelgrain is kept separate from the slotted, single perforate, internalburning oxidizer charge, and

FIG. 2 illustrates a single perforate, internal burning pressedpolyethylene coated lithium aluminum hydride fuel disk with a restrictorcoating, and

FIG. 3 illustrates a web of pressed polyethylene coated lithium aluminumhydride fuel disks in a lucite holder. 7

Referring to FIG. 1, the drawing shows the structure of the type ofpropellant grain which was employed in the tests run to compare theperformance of the bipropellant system with the monopropellant. Theoxidizer charge is a slottedintemal burning grain placed at the head ofthe composite grain so that theoxidizers products of combustion, hightemperature reactive gases, pass over the surface of the fuel graincausing it to decompose and to then react with the oxidizers products. v

The pressed lithium aluminum hydride fuel grain configuration shown inFIG. 2 did not burn out. When this fuel grain was fired with theslotted, single perforate oxidizer, the burning surface of the fuelgrain which was exposed to the oxidizers products of combustion wasinsufficient to permit complete consumption.

Referring to FIG. 3, the pressed lithium aluminum hydride fuel grain ofdisks or plates shown, was consumed at a slow rate during combustion.When this fuel grain was fired with the oxidizer, the burning surface ofthe grain which was exposed to the oxidizers products of combustion wasgreater than the configuration in FIG. 2 and permitted completeconsumption at a slow rate. Thus, it is seen that thesurfaces over whichthe oxidizer propellant products of combustion pass are more readilyconsumed than those surfaces normal to the direction of gas flow.

Propellants currently in use or under active development fall into the240-265 second specific impulse class. Future demands on performancewill require propellants of the 280 second specific impulse class orgreater. To fulfill these increased demands more potent fuels, such aspowerful reducing agents of the metallic erting one or both of thecomponents so that they will not react until commanded. A protectivecoating around each particle achieves, in part, at least, some measureof protection, however, it does not always maintain its protectivecharacter through mixing, storage and handling up to the time of firing.

A new technique which will provide maximum safety is now proposed. Thefuel component and the oxidant component which have been incorporatedinto the same matrix in the past now affixed in the engine in twoseparate and distinct packages, a solid bipropellant. Thus, one packagewould contain an oxidant while the other package would contain a fuel.By this arrangement the two troublesome components are separated at alltimes during mixing, storage, and subsequent handling. To get thefueland oxidant together at the time of firing or rather to bringtogether their products of decomposition, the oxidant package mustrelease oxygen rich products of combustion and the fuel package mustrelease fuel rich products of decomposition, both at a known andpredictable rate so that a reaction will occur in an efficient manner.

The most critical factor affecting the release and subsequentcombination of the products of combustion is the geometry of the fuelgrain with respect to that of the oxidizer grain. In order to have thefuel consumed at-a reasonable linear rate, the fuel grain geometry, withrespect to the oxidizer grain, must be of such a configuration that thefuels surface being consumed is in the main stream of the oxidizersproducts of combustion. To effect this action, several grain geometrieswere investigated for the performance studies of the bipropellant. Amonopropellant and a standard DDP- propellant were used as controls. Thesimplest and most satisfactory grain design under the circumstances wasa one-eighth inch slotted, 0.6 inch diameter single perforate, internalburning grain'which was used for the design of the monopropellant, theDDP-70 grain design was essentially completely consumed during theburning of the oxidizer grain. The designs of the pressed polyethylenecoated lithium aluminum hydride shown in FIG. 2 and '3 which were testedwere disks 1 35 inches in diameter and one-half inch and one-eighth inchthick, respectively.

In evaluating grain design, it was found that the end surfaces of thegrain could be neglected so that the computed burning surface of thefuel grain was only that surface parallel to the axis of the motor. Itis recognized that the grain geometries employed were selected on thebasis of rather simplified assumptions regarding the mode of consumptionof the fuel grain and therefore the conditions under which theexperiments were conducted were other than optimum. The specific impulsevalues therefore obtained do not indicate the maximum efficiencypossible. Greater efficiency may be obtained with other arrangements ofthe bipropellant components, such as, for example, placing the fuelgrain between the two oxidizer grains so that the first oxidizer wouldcause the fuel grain to be consumed and the second oxidizer would act asan afterbumer delivering the desired products of combustion to thenonle.

While it is to be understood that the present invention is not drawn toany particular composition but places novelty upon the idea ofseparating a solid fuel package from an incompatible solid oxidizerpackage, a few examples of the compositions used in these tests are setforth merely as guides for workers in the art and are not to beconsidered limiting in any way. The following compositions were employedin tests conducted in connection with this invention.

BIPROPELLANT Oxidizer Weight Percent Nitroglyeerine 32.1%

Ammonium Perchlorate 56.1%

Polyurethane 1 1.8% 100.0%

Fuel

Magnesium 73.0%

Polyurethane 24.9%

Carbon Black 2.1% 100.0%

Fuel/oxidizer ration 1:4

MONOPROPELLANT Nitroglycerine 26.75%

Ammonium Perchlorate 46.75%

Polyurethane 13.98%

Magnesium 12.17%

Carbon Black 0.35%

DDP-7O Powder Nitrocellulose (13.15N) 30.0%

Nitroglyccrine 10.0%

Ammonium Perchlorate 28.0%

Aluminum 29.0%

2 nitrodiphenylamine 1.0

Resorcinol 2.0% 100.0%

Solvent Nitroglycerine 70.0%

Triacetin 29.0%

2 nitrophenylamine 1.0% 100.0%

Powder/Solvent 72/28 Pressed polyethylene coated lithium aluminumhydride disks illustrated in FIGS. 2 and 3 were fired with the abovebipropellant oxidizer composition.

A specific impulse of 275-279 seconds was predicted for fuel/oxidizerratios over the range of 25/75 to 35/65.

Binders may be used, and in the case of metallic hydrides and powderedoxidizers, are necessary, to put the ingredients into useful forms. Thebinders must be carefully chosen so that they do not react with themetal hydride. This precludes, in general, binders which contain oxygen,halides and carbon to carbon double bonds. The fuel package having theserestrictions will not be self consuming, and thus the geometry of thefuel must be such that the products of the oxidants combustion will passover the fuel to effect combustion of the latter.

All firings were made in a two inch static test motor in the rangefacilities of the Interior Ballistics Laboratory. Graphite nozzles wereused with an expansion ratio of six and a divergent half angle of 10.Each firing was monitored with two Dynamic Instruments Co., Inc., ModelTCPT 31 SP-35, 0-3000 psi pressure gauges and a double AlleghanyInstrument Company, Alinco Load Cell, Model 3441,000 lbs. All roundswere ignited with a US. Flare Squib 107-A and 3 grams of FFFG blackpowder.

The average results of several test runs which were made are'set forthin the following table for comparison.

The comparison between the solid bipropellant firing results and themonopropellant firing results appeared to be quite good. The solidbipropellants average measured specific impulse corrected to standardconditions is 96 percent of the monopropellants average measuredspecific impulse corrected to standard conditions and the averagemeasured characteristic velocity of the solid bipropellant is 98 percentof the monopropellants average characteristic velocity. Thisdemonstrates that the combustion and performance of the two-packagepropellant, i.e., the bipropellant, can be achieved with goodefficiency. Better efficiencies are undoubtedly possible with morerefined fuel grain geometries, however, these tests proved thefeasibility of the principal of separation of fuel and oxidizer in apropellant grain.

Of course, it is to be understood that the present concept may beequally applicable to compatible ingredients as well as to incompatibleingredients. These grain designs are only exemplary, and numerousmodifications are possible so long as the basic concept of theseparation of fuel and oxidizer into distinct packages is maintained.

We claim:

pulse of over 275 seconds, comprising a slotted, single perforate,internal burning oxidizer grain and pressed lithium aluminum hydrideplates adjacent thereto having their longitudinal axes parallel to thedirection of

2. A solid bipropellant grain having a specific impulse of over 275seconds, comprising a slotted, single perforate, internal burningoxidizer grain and pressed lithium aluminum hydride plates adjacentthereto having their longitudinal axes parallel to the direction of gasflow.